[Intel-gfx] [PATCH] drm/i915: Avoid context dereference inside execlists_submission_tasklet

[Michel Thierry]

On 12/19/2017 2:09 PM, Chris Wilson wrote:
> A lesson that has to be relearnt over and over again is that the request
> does not keep a reference to the context and so we cannot freely
> dereference the context from inside the execlists_submission_tasklet. In
> particular, we try to do so in the new GEM_TRACE() so convert those over
> to the port->context_id we keep for GEM debugging. This means the
> tracing now depends on DRM_I915_GEM_DEBUG.
> 

Even before the port->context_id dependency, I don't think many people 
would enable DRM_I915_TRACE_GEM without DRM_I915_DEBUG_GEM.

> Fixes: bccd3b831185 ("drm/i915: Use trace_printk to provide a death rattle for GEM")
> References: https://bugs.freedesktop.org/show_bug.cgi?id=104066
> References: https://bugs.freedesktop.org/show_bug.cgi?id=104162
> References: https://bugs.freedesktop.org/show_bug.cgi?id=104242
> References: https://bugs.freedesktop.org/show_bug.cgi?id=104310
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/Kconfig.debug | 2 +-
>   drivers/gpu/drm/i915/intel_lrc.c   | 6 +++---
>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> index fa36491495b1..c846b250b9c4 100644
> --- a/drivers/gpu/drm/i915/Kconfig.debug
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -29,7 +29,6 @@ config DRM_I915_DEBUG
>          select SW_SYNC # signaling validation framework (igt/syncobj*)
>          select DRM_I915_SW_FENCE_DEBUG_OBJECTS
>          select DRM_I915_SELFTEST
> -       select DRM_I915_TRACE_GEM
>           default n
>           help
>             Choose this option to turn on extra driver debugging that may affect
> @@ -55,6 +54,7 @@ config DRM_I915_TRACE_GEM
>          bool "Insert extra ftrace output from the GEM internals"
>          select TRACING
>          default n
> +       depends on DRM_I915_DEBUG_GEM
>          help
>            Enable additional and verbose debugging output that will spam
>            ordinary tests, but may be vital for post-mortem debugging when
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index eee718e3f371..64d49d5054b9 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -449,7 +449,7 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
> 
>                          GEM_TRACE("%s in[%d]:  ctx=%d.%d, seqno=%x\n",
>                                    engine->name, n,
> -                                 rq->ctx->hw_id, count,
> +                                 port[n].context_id, count,
>                                    rq->global_seqno);
>                  } else {
>                          GEM_BUG_ON(!n);
> @@ -861,7 +861,7 @@ static void execlists_submission_tasklet(unsigned long data)
>                           */
> 
>                          status = READ_ONCE(buf[2 * head]); /* maybe mmio! */
> -                       GEM_TRACE("%s csb[%dd]: status=0x%08x:0x%08x\n",
> +                       GEM_TRACE("%s csb[%d]: status=0x%08x:0x%08x\n",
>                                    engine->name, head,
>                                    status, buf[2*head + 1]);
> 
> @@ -905,7 +905,7 @@ static void execlists_submission_tasklet(unsigned long data)
>                          rq = port_unpack(port, &count);
>                          GEM_TRACE("%s out[0]: ctx=%d.%d, seqno=%x\n",
>                                    engine->name,
> -                                 rq->ctx->hw_id, count,
> +                                 port->context_id, count,
>                                    rq->global_seqno);
>                          GEM_BUG_ON(count == 0);
>                          if (--count == 0) {
> --
> 2.15.1
> 

Reviewed-by: Michel Thierry <michel.thierry at intel.com>